1. Field of the Invention
The present invention relates generally to methods for blending additive components comprising dispersant additives and overbased alkaline earth metal detergent additives into base oil to obtain a lubricating oil additive concentrate ("D/I" package) in which the dispersant and overbased detergent have improved compatibility. More particularly, the invention relates to a method for improving the DI package compatibility of the dispersant and the basic magnesium containing detergents which comprises the steps of: (1) preparing a mixture comprising (a) the dispersant; (b) the detergent; and (c) a substantially inert solvent; and (2) blending said mixture at a temperature within the range of about 150.degree. F.-380.degree. F. for a period of time sufficient to render the mixture substantially free of haze and sediment, said method being subject to the proviso that the mixture prepared in step (1) be free of other additive ingredients susceptible to thermal decomposition in the blending of step (2). The pre-blended mixture of dispersant and detergent, when blended with other DI package additives such as oxidation inhibitors, wear inhibitors, etc., results in a DI package having little or no haze and sediment, both initially and on aging.
2. Discussion of Prior Art
Modern day crankcase lubricants for passenger car as well as heavy duty engines must incorporate a variety of highly specialized additives to meet exacting performance standards promulgated under the American Petroleum Institute's "SF" and "SG" classification for passenger car or under the "CD" and "CE" classification for heavy duty diesel engines.
The additives typically incorporated in a finished lubricant include dispersants, detergents, oxidation inhibitors, wear inhibitors, etc. Dispersants help keep the engine clean by keeping dirt and other particles in suspension in the motor oil to prevent their being deposited or baked onto piston surfaces as "varnish" or onto internal engine surfaces as "sludge". Because dispersing power alone is not sufficient to prevent formation of deposits in the engine, strong detergents capable of cleaning and dissolving deposits on engine surfaces are also required. The detergents normally used for this purpose are the neutral or overbased oil soluble alkaline earth metal sulfonates, phenates and salicylates. If the sulfonates are overbased, so as to contain an excess of basic alkaline earth metal over that necessary to neutralize the sulfonate, the detergent can also act to neutralize the acidic products of combustion which further promotes engine cleanliness.
The conventional manufacture of commercial lubricants incorporating a combination of specialized additives is typically carried out by introducing the additives to the oil in the form of a single additive "package" containing about from 10 to about 80 wt. % active additive ingredients dissolved in hydrocarbon oil or other suitable solvent. To prepare the finished lubricant, the additive package concentrate can be diluted with anywhere from about 3 to about 40 parts by weight of a suitable lubricating oil per part by weight of the additive concentrate.
Although the use of additive package concentrates simplifies handling and shipping of the additives and facilitates solution or dispersion of the additives in the final lubricant blend, a well known problem with such packages is the tendency of certain types of additives to interact with one another. Such interaction is evidenced by the formation of undesirable haze and sediment in the additive package concentrate and can seriously effect the performance and aesthetic qualities of the finished lubricant. This additive interaction is particularly pronounced in packages having a basic magnesium containing detergent and an ashless lube oil dispersant. One way of reducing the interaction of the dispersant and the detergent is to blend other additives with the dispersant before adding the detergent. While this approach is somewhat successful, need presently exists for an improved blending procedure capable of minimizing even further the dispersant detergent interaction.
Robson U.S. Pat. No. 4,502,971 discloses that the problem of interaction between dispersants and basic magnesium detergents can be reduced if the dispersant is prereacted with a basic salt containing an alkali metal such as sodium. The invention described below, however, differs from the Robson '971 patent by providing improved dispersant/detergent compatibility without need for introduction of sodium.